1. Field of the invention
The present invention relates to a sewing machine with a bobbin thread monitor and more particularly, to a sewing machine with a bobbin thread monitor for indicating an amount of thread remaining on a bobbin.
2. Description of Related Art
A conventional sewing machine with a bobbin thread monitor is disclosed, for example, in Japanese Utility Model Laid-Open Publication (Jikkaisho) No. 61-180685. According to the bobbin thread monitor, when a rotating hook ceases rotating, a light detector irradiates the circumferential surface of a bobbin winder spindle with a light. The light reflected by the circumferential surface of the bobbin winder spindle is detected by the light detector. Based on the intensity of the detected light, the bobbin thread monitor detects an amount of thread remaining on a bobbin.
The above-mentioned bobbin thread monitor, however, cannot accurately detect the amount of thread remaining on the bobbin when dust or oil adheres to the light detector.